Conventionally, ships and lifeboats are equipped with a Search And Rescue Transponder (SART). When the power of the SART is turned on in a distress situation, in response to receiving a radar wave in 9 GHz band from a ship or an aircraft, the SART transmits a distress (SOS) signal (SART distress signal) in the same 9 GHz band. This SART distress signal is a pulsed response signal formed by frequency sweep in a sawtooth form. Since a reception bandwidth of a ship radar is set so that the frequency sweep band of the distress signal traverses it, the radar apparatus can receive the distress signal as a pulse with a constant interval, and the SART distress signal is expressed in a radar image as a plurality of short points in a distance direction from the SART position.
As a radar apparatus which detects the SART distress signal as described above, for example, a radar apparatus disclosed in Patent Document 1 is known. In this radar apparatus, whether a SART distress signal is issued is determined by cross-correlating a signal at a constant cycle which is substantially the same as that of the SART distress signal with detection data detected by the radar apparatus.